There are situations in which environmental sound is to be blocked from a person's ear while controlled sound is delivered to the ear. One situation is a communication system for use in a noisy environment, and another is a hearing test. Instead of using ear cups or earmuffs with speakers in them, a speaker can be coupled to a through hole in a simple and low cost earplug. Such earplug can be of the type worn by workers in noisy environments such as factories, but with a passage to carry sound.
One way to construct such an earplug with a passage in it, or in-ear device, is by modifying a foam elastomeric earplug of the type that is worn by workers in noisy environments such as factories to block sound. In such modification of an existing earplug, a hole is punched through the earplug to leave a passage that extends along the length of the earplug. A tube is inserted into the passage and is held in place as by adhesive. The punching of a passage in an elastomeric earplug can leave a somewhat irregular passage extending through the earplug. Adhesive applied to the tube tends to wipe off as the tube is inserted into the earplug passage, leaving an even more irregular in-ear device and with the bonding being uncertain.